Hey,
I don't know if this is an isolated problem, or if it has something to do with the IP address of the user's, but when I run Tremulous, and my friend does on his computer at my house (same router), it crashes the second player to join if we join the same server. It works for a good 30 seconds, maybe even longer, but eventually Tremulous encounters a problem and must be shut down.
Any known way around this?